1. Field of Invention
The present invention relates to a bonding method using spherical bodies made of silicon rubber.
The present invention also relates to a method for manufacturing a structure (structural body) with a closed space, and particularly relates to a method for manufacturing a structure with a closed space in which a structure with a closed space made of a fiber reinforced resin composite material is formed integrally by bonding without using any mechanically coupling unit such as rivets, so that the labor and cost for manufacturing can be reduced, and the manufacturing cycle can be accelerated.
The present invention also relates to a method for manufacturing a composite material stiffened panel, and particularly relates to a method for manufacturing a composite material stiffened panel by use of a flexible mandrel.
The present invention also relates to a method for manufacturing a structure with a closed space.
2. Description of Related Art
Various methods for bonding adherends with each other by use of a bonding adhesive have been heretofore proposed and put into practical use in various industries of transport equipment such as aircraft, automobiles, ships, and so on, or general industries. Bonding is generally carried out through the following steps: (1) a surface treatment step of carrying out surface treatment on bonded surfaces of adherends; (2) a bonding adhesive application (pasting) step of applying (pasting) a bonding adhesive onto the bonded surface of one of the adherends or the bonded surfaces of both of the adherends; (3) a lamination step of laminating the adherends to each other; (4) a retaining step of pressing the laminated adherends to thereby fix (retain) these adherends; and (5) a bonding adhesive hardening step of hardening the bonding adhesive by heating or curing.
Here, the retaining step (4) is an essential step for forming an optimal bonding adhesive layer and eliminating bubbles mixed into the bonding adhesive, and it is demanded for applying uniform pressure to the laminated adherends. The retaining step (4) is usually carried out in parallel with the bonding adhesive hardening step (5) until hardening of the bonding adhesive is completed. For example, when an aircraft component is manufactured, retaining and hardening of a bonding adhesive are carried out concurrently by use of a pressure vessel called an autoclave which can carry out pressurizing and heating. Alternatively, a C-clamp (see FIG. 26) or a pressing machine (see FIG. 27) is generally used for pressing.
Although the autoclave used in the process of manufacturing aircraft components was indeed effective in applying uniform pressure even to curved bonded surfaces of the components, the cost for constructing the equipment or the operation cost was high because the autoclave was large in scale and had a special structure. Accordingly, the autoclave was not suitable for bonding compact components with each other or for bonding general-purpose components with each other because the cost increased too much.
On the other hand, when a C-clamp 410 as shown in FIG. 26 was used, a pressurizing portion 411 applied pressure to only a part of adherends 430 so that uniform pressure could not be applied all over the adherends 430. In addition, when the pressure was applied, a bonding adhesive in the pressurized portion of the adherends 430 might be pressed and flow to the surroundings. When volume contraction occurred due to the hardening reaction of the bonding adhesive after then, the bonding adhesive in this pressurized portion might become thin so that sufficient bonding could not be obtained.
On the other hand, when the bonding adhesive was heated and hardened concurrently with pressing, a clamp arm 412 of the C-clamp 410 might be thermally expanded and the pressurizing portion 411 was moved in a direction opposite to the pressurization direction so that sufficient pressure was not applied to the adherends 430. In addition, although the pressurizing portion 411 was moved up and down by a screw or the like so as to apply pressure to the adherends 430, the magnitude of the pressure at that time (hereinafter referred to as “pressurizing value”) was not known. Thus, suitable magnitude of pressure could not be applied in accordance with the adherends or the kind of bonding adhesive.
On the other hand, a pressing machine 420 as shown in FIG. 27 was effective in bonding adherends 430 with each other, when the bonding adherends 430 had planar bonded surfaces respectively. However, when adherends having curved bonded surfaces were bonded with each other, upper and lower pressure plates 421 and 422 had to be produced to match the curved bonded surfaces of the adherends 430. Thus, the manufacturing cost thereof increased.
By the way, Aircraft or space structures are desired to be structurally high in strength and light in weight from the point of view of special characteristics of application of the aircraft or space structures. To this end, when wings, enpennage, a fuselage, and so on, of an aircraft are formed, a semimonocoque structure by which a load mainly is applied to a shell member is adopted. Wings of an aircraft can be taken as representative examples of such a semimonocoque structure. A wing of an aircraft is constituted by a leading edge portion, a wing box and a trailing edge portion. Of them, the inter-spar portion has a box-shaped structure constituted by a front spar, a rear spar, upper and lower skins, stringers, ribs, etc.
Some methods for forming a structure having a closed space internally like the box-shaped structure have been proposed. The methods include (1) a method in which plate-like bodies 510 prepared by used of a metal material or a composite material are used to form a rectangular parallelepiped box-like body 520 having an open portion 521 as shown in FIG. 28, an upper portion plate-like body 530 is disposed on the upper portion of a flange 522 provided in the open portion 521, and the flange 522 and the upper portion plate-like body 530 are coupled with each other by use of mechanical coupling units (rivets) 540 as shown in FIG. 29; and (2) a method in which two rectangular parallelepiped box-like bodies each having an open portion are formed by use of a plurality of combination mandrels in an RTM method (Resin-Transfer-Molding), and the open portions of the two box-like bodies are coupled by use of mechanically coupling units.
However, according to the method (1), as shown in FIGS. 28 and 29, complicated works were required. Such complicated works included the work of forming rivet holes in the flange 522 provided in the open portion 521 of the box-like body 520 and in the circumferential edge portion of the upper portion plate-like body 530, and the work of fastening rivets. In addition, when a large-sized structure such a sawing box portion of an aircraft was formed, a large number of rivets 540 were required to result in increase of the weight, contrary to the request of reduction in weight. Further, the cost to manufacture the rivets 540 was required separately.
On the other hand, according to the method (2), the open portions of the box-like bodies had to be coupled by rivets so that there arose problems similar to those in the method (1). That is, works were complicated, the weight of the structure increased, and the cost increased. In addition, metal mandrels matching the shape of the structure had to be used. Accordingly, a large number of metal mandrels different in shape had to be prepared. Further, in the heating step using the RTM method, the molded box-like bodies were contracted thermally. Accordingly, the work (demolding work) for extracting the metal mandrels from the insides of the box-like bodies was so difficult that the manufacturing cycle was delayed.
By the way, to meet the demands of lighter weight and higher strength in aircraft in the aerospace field, aircraft structures are often manufactured by use of fiber reinforced plastics in recent years. For example, a stiffened panel 610 to be incorporated in a wing of an aircraft as shown in FIG. 30 is manufactured by molding a skin 611 and stiffenerss 612 individually and then coupling them by fasteners or bonding them by a bonding adhesive. As the method for molding the skin 611, there is employed a method in which prepregs are laminated and hardened; or a method in which thermosetting resin is impregnated into reinforced fiber and hardened.
The following method is also employed. That is, a prepreg laminated to the skin 611, and stiffenerss 612 primarily hardened in advance are laminated through a bonding adhesive. Bagging films are inserted into spaces (hollow portions) surrounded by the stiffeners 612 and the prepreg for the skin 611 respectively. After then, the stiffeners 612 and the prepreg for the skin 611 are covered with a bagging film. The air is evacuated from the bagging film while the bagging film is pressed and heated from its outside so as to harden and mold the prepreg for the skin 611 and the stiffeners 612. Thus, the stiffened panel 610 is manufactured.
On the other hand, examples of the method for manufacturing a movable wing 620 such as an aileron, a flap or a tab by use of a fiber reinforced composite material may include: a method in which prepregs for a leading edge portion 621, a spar portion 622 and a skin portion 623 are laminated and hardened, then disposed in predetermined positions, and coupled by fasteners or bonded by a bonding adhesive; and a method in which fiber reinforced fabric materials for a leading edge portion 621, a spar portion 622 and a skin portion 623 are set in a molding jig, and thermosetting resin is introduced thereto from the outside, impregnated therein and hardened, as shown in FIGS. 31A and 31B.
Also when the movable wing 620 is manufactured, divisible mandrels made of metal or hard rubber are inserted into a front hollow portion 630 formed by a leading edge portion 621 and a spar portion 622, and a rear hollow portion 640 formed by the spar portion 622 and upper and lower skin portions 623 (see FIG. 31B). When the respective hollow portions 630 and 640 have complicated curved internal surfaces, bagging films are inserted into the respective hollow portions 630 and 640 so as to introduce compressed gas thereto. Thus, the shapes of the leading edge portion 621, the spar portion 622 and the upper and lower skin portions 623 are prevented from being deformed by the application of pressure at the time of resin hardening, while the thermosetting resin is prevented from flowing into the respective hollow portions 630 and 640.
However, when the stiffened panel 610 was manufactured, the shapes of the bagging films were not stable, so that it was difficult to dispose the bagging films accurately to match the internal shapes of the hollow portions. When the bagging films were not disposed accurately to match the internal shapes of the hollow portions, the pressure applied to the prepreg or the fiber reinforced fabric material might be uneven when the thermosetting resin was hardened. Thus, the product quality was deteriorated. Further, at the time of molding, the bagging films might be bored so that pressurization was impossible, or the bagging films might be broken to be left in the hollow portions when they were removed. Further, the bagging films had to be exchanged in every manufacturing process, so that the cost increased.
On the other hand, when the mandrels made of metal were used to manufacture the movable wing 620, the hollow portions had to be formed to have constant or one-directionally tapered shapes so that the metal mandrels could be extracted after the molding. Accordingly, the product shape was limited. In addition, when the shapes of the metal mandrels were disordered slightly in accuracy, it was difficult or impossible to extract the metal mandrels from the hollow portions. Therefore, extremely stringent processing accuracy was required so that the manufacturing cost for the metal mandrels increased. Further, the metal mandrels were so heavy that they were difficult to handle.
On the other hand, the mandrels made of hard rubber were light in weight and did not need stringent processing accuracy in comparison with the metal mandrels. However, the thermal expansivity of rubber was so high that excessive pressure might be applied to thin portions of the prepreg or the fiber reinforced fabric material by the expansion of the hard rubber mandrels in accordance with heating when the thermosetting resin was hardened. Thus, the product quality might be deteriorated.
By the way, aircraft or space structures are desired to be structurally high in strength and light in weight from the point of view of special characteristics of application of the aircraft or space structures. To this end, when wings, enpennages, a fuselage, and so on, of an aircraft are formed, a semimonocoque structure by which a load mainly is applied to a shell member is adopted. Wings of an aircraft can be taken as representative examples of such a semimonocoque structure. A wing of an aircraft is constituted by a leading edge portion, a wing box portion and a trailing edge portion. Of them, the wing box portion has a box-shaped structure constituted by a front spar, a rear spar, upper and lower skins, stringers, ribs, etc.
Some methods for forming a structure having a closed space internally like the box-shaped structure have been proposed. The methods include a method in which a box-like body having an open portion is prepared, a skin is disposed on the upper portion of a flange provided in the open portion, and the flange in the open portion and the skin are coupled with each other by use of a mechanical bonding unit (fastener); and a method in which two box-like bodies each having an open portion are molded by use of a plurality of combination mandrels, and the open portions of the two box-like bodies are coupled.
However, according to the method using a fastener, stress was concentrated in the coupling portion where the fastener was used. Thus, there was a problem in fatigue characteristics. In addition, the fastener was generally made of metal, resulting in increase in weight and cost of the structure. On the other hand, according to the method using mandrels, it was necessary to couple the open portions of the box-like bodies with each other through a fastener finally. Thus, there occurred similar problems such as stress concentration, increase in weight and cost of the structure as described above. In addition, efforts were required for the work (demolding work) to extract the mandrels from the insides of the box-like bodies.
To solve such problems, the following method has been proposed. That is, a box-like body is filled with a predetermined amount of beads made of silicon rubber being superior in thermal expansivity. A skin is disposed on a flange in an open portion of the box-like body through a bonding adhesive. The silicon rubber beads are heated together with the box-like body and the skin so that the silicon rubber beads are thermally expanded. As a result, pressing force is applied from the inside of the box-like body to the outside thereof. Thus, the box-like body is bonded with the skin.
However, according to the method using beads made of silicon rubber, the filling amount or the initial pressing rate of the silicon rubber beads as pressure media had to be established precisely in order to obtain proper bonding pressure.
Further, as a method for bonding a plurality of constituent parts in combination so as to form a box-like body, there has been a method using a pressure bag (see Japanese Patent Laid-Open No. 58-205730). In this method, a plurality of constituent parts for constituting a box-like body are combined, wholly covered with a packing material (pressure bag made of silicon rubber), and then pressurized so that the respective constituent parts are bonded. The method is applied to the case where a box-like body is pressure-molded out of an impregnated prepreg in an autoclave.
However, according to the bonding method using a pressure bag, a special jig was required because it was necessary to mold the pressure bag correspondingly to the inner surface shape of the box-like body to be formed. Thus, the cost increased and a space for storing and managing the special jig was required. In addition, when the box-like body to be formed had a complicated inner surface shape, the shape of the pressure bag also became complicated. Thus, not only was it difficult to mold the pressure bag, but there also occurred a problem in durability thereof. Further, the work to bring the pressure bag into tight contact with the inner surface of a product was complicated.